Understanding dengue’s resurgence in Bangladesh and approaches to combat it.
In 2023 a public health emergency loomed over Bangladesh – a widespread outbreak of Dengue fever. The World Health Organization (WHO) raised an alarm, issuing alerts and global situation reports detailing the surge in dengue cases worldwide. Data records indicate a rise in reported cases globally between 2000 and 2019. Following a brief respite in cases during 2020-2022, likely due to the observed lockdowns and social distancing maintained in response to the COVID-19 pandemic, the year 2023 saw a worrying resurgence of dengue fever. This alarming uptick was unlike anything seen before, marked by a dramatic rise in the number of outbreaks, their size, and their widespread occurrence across multiple regions, even reaching areas that hadn’t previously been affected by dengue. The 2023 outbreak in Bangladesh was particularly severe, with an unprecedented spike in cases, stretching the healthcare system and resources to the limit.
2023 DENGUE IN NUMBERS
The 2023 outbreak saw record-breaking dengue cases, both in terms of fatalities and hospitalisations. Historically, dengue outbreaks were primarily concentrated in Dhaka, but the 2023 outbreak spread rapidly nationwide, with the number of cases reported outside the capital doubling at cases compared to past years. The country witnessed a staggering 321,179 hospitalisations and a distressing 1,705 fatalities from 1 January to 31 December, surpassing the cumulative death toll of the previous 23 years combined.
The outbreak took a dramatic turn for the worse in July 2023, with 43,854 new cases reported that month alone. The situation escalated further in September, marking the peak of Bangladesh’s dengue outbreak, recording the highest single-month cases at 79,598 and the highest fatalities at 396, making it the deadliest period.
Experts believe that a lack of coordinated efforts from, and governance across relevant government agencies was a major failure point that severely hampered successful dengue management efforts. The absence of an established vector management policy which intends to control the Aedes mosquito population, the primary carrier of dengue, is seen as another key shortcoming. The lack of a clear plan and data-driven decision-making due to the missing policy are viewed as critical failures. Furthermore, a limited surveillance system which fails to capture a nationwide geographic-based overall picture of the dengue outbreak is another shortcoming that the outbreak revealed. Notably, weak surveillance systems may often cause delayed reporting, response, and identification of symptoms, contributing to elevated severe dengue outcomes.
WHY 2023 WAS SO FATAL
The escalating risk of the rampant transmission of a dengue epidemic can be attributed to a convergence of circumstances or factors. For instance, climatic changes played a significant role in this crisis. The El Niño phenomenon of 2023 brought about rising temperatures, increased rainfall, and high humidity levels – conditions that created an ideal breeding ground for the primary vectors of the dengue transmission – Aedes aegypti and Aedes albopictus. Such a climatic shift not only allowed the mosquito population to thrive and proliferate but also spread to previously unaffected regions, exposing naive populations to the virus.
Political and financial instabilities, coupled with mass population movements often compound the challenges of containing the outbreak or preventing its spread across borders. Unplanned urbanisation, specifically in densely populated cities like Dhaka, contributed significantly to the outbreak’s intensity. Further aggravating the dengue crisis are poor waste management systems, clogged drainage, and the accumulation of stagnant water in containers and basements, which provide ample breeding sites for mosquitoes. Surge in the risk of dengue virus transmission also occurs when mosquito breeding sites are located in close vicinity to residential dwellings. Most importantly, the changing distribution of the primary dengue vectors, particularly their advancement into naive populated regions raises concerns about the potential for the epidemic to gain a stronger foothold globally.
In Bangladesh, all four different serotypes of the dengue virus have been found circulating among the population. However, not all dengue cases have been thoroughly tested and analysed (serotyped) to determine the specific virus type responsible for the infection, leaving gaps in our understanding of the dynamics at play. While serotype 3 was predominant in the early 2000s, serotypes 1 and 2 emerged between 2013 to 2016, and more recently, serotypes 2 and 3 have been co-circulating. The WHO warns that shifts in dominant serotypes may contribute to increased severity and hospitalisation rates when individuals are infected with a different serotype than their previous exposure, triggering more intense immune responses. Echoing WHO’s concerns, Bangladeshi experts point to shifting dominant serotypes and the dramatic climate shifts brought on by El Niño as potential culprits behind the severity of the winter outbreak and year-round prevalence of dengue.
Confronting the interrelated factors that fuel dengue transmission is imperative for curbing the threat of recurring outbreaks and safeguarding the health of Bangladesh’s citizens. The mosquito control approach adopted by the Bangladesh government currently relies on the use of insecticides through fogging during the vector season and spraying of larvicide in the drainage system to control Culex mosquitoes. However, these techniques to eliminate their breeding grounds prove to be ineffective. Additionally, weak surveillance and an underprepared healthcare system at the local level hinder effective management.
2024 DENGUE OUTLOOK AND PREPARATION
Bangladesh braces for a potentially worse dengue season in 2024. As of April 2024, there has been a total of 1,252 affected and 16 deaths. Public health experts, entomologists, and doctors worry that the brutal outbreak of 2023 may be a mere prelude, with factors like insufficient mosquito control efforts, stretched healthcare resources, and the early arrival of monsoon rains cultivating the ideal breeding habitats for the virus transmitters. While Dhaka bore the brunt of the crisis last year, outlying regions are now particularly at risk, raising fears of a wider geographic spread. These early downpours paint a worrisome picture, potentially triggering a surge in mosquito populations and setting the stage for devastating outbreaks. With these factors converging, Bangladesh appears headed for a challenging year in the ongoing fight against dengue.
The centralised structure of the healthcare management system in Bangladesh is a major bottleneck in the prevention of such a public health crisis. Hence, Bangladesh should begin by shifting its focus from its capital Dhaka to establish well-equipped facilities throughout the country, particularly in remote areas to improve the outbreak response. On a community level, education about risk reduction, prevention measures, and early warning signs is essential to foster proactive participation in outbreak management. Moreover, providing free insecticide-treated bed nets can significantly enhance individual protection against mosquito bites. Engaging volunteers like student groups and local leaders in mosquito breeding site eradication can also substantially reduce mosquito populations.
Mosquito control poses a formidable challenge, even for countries with functioning control programs. Hence, to optimise its effectiveness, vector control initiatives must target all potential human-vector contact points. This encompasses not just residential areas but also workplaces, schools, and hospitals, where the risk of transmission remains elevated. The Integrated Vector Management Strategy (IVM) by the World Health Organisation (WHO) provides a comprehensive framework for dengue outbreak control. This approach combines several tactics to target mosquitoes at various stages of their life cycle: eliminating stagnant water sources that serve as breeding grounds, strategically applying WHO-approved larvicides in non-potable water to kill mosquito larvae, and utilising indoor residual spraying of insecticides within homes and buildings to target adult mosquitoes. Additionally, promising new technologies like Wolbachia, which reduces mosquito capacity to transmit dengue and environmentally friendly larvicides like Bacillus thuringiensis israelensis (B.T.I) are worthy of consideration and evaluation for possible incorporation into the overall vector control strategy.
